1. Field of the Invention
The present invention is directed generally to apparatus, methods and procedures for improved diagnostic imaging and, more particularly, to a system and method for improved reliability and patient comfort in diagnostic imaging.
2. Description of the Related Art
Breast cancer screening techniques have concentrated on the process of mammography because screening technique need to be economical in order to achieve widespread use. However mammography often has a high incidence of false positive readings that often prove to be benign or fluid-filled cysts that do not require surgical intervention or other highly invasive therapeutic procedures. It is widely accepted that late-stage breast cancer detection is associated with significantly increased morbidity and mortality. Despite extensive research, new diagnostic classification systems and improved detection methodologies, there is still a great need to detect small neoplasms (typically 5 mm or smaller) accurately, quickly, noninvasively and inexpensively and with a good idea of size during the early detection process. Failure to detect such early breast cancers is associated with more invasive therapeutic interventions at higher risk and higher expense.
One alternative to X-ray mammography is conventional, reflective ultrasound using a pulse-echo technique. Generally, breast sonograms using reflective ultrasound are used to characterize masses (such as whether they are cystic or solid) detected by physical exam or by mammography. There is still debate within this field whether reflective ultrasound is able to accurately predict benign from malignant solid masses. Moreover, reflective ultrasound is operator-dependent and time-consuming. Further, sonography is not useful for the assessment or detection of micro calcifications, often the only sign of early in situ ductal carcinomas.
Another alternative is to use a through transmitted plane wave of ultrasound energy to pass through the anatomy and thus carry with it the phase and amplitude information about the anatomy. This, however, is a complicated set of data since it represents three-dimensional information of the internal structure of the anatomy. A demonstrated method of converting this set of dynamic data into a useful image is through the use and application of acoustical holography as disclosed in the referenced prior art patents and patent applications.
Ultrasonic holography as typically practiced is illustrated in FIG. 1. A stimulus wave of sound 1a (i.e., ultrasound) is a plane wave that is generated by a large area object transducer 1. Such a transducer is described in U.S. Pat. No. 5,329,202. The sound is scattered (i.e., diffracted) by structural points within the object. The scattered sound 2a from the internal object points that lie in the focal plane 2 are focused (i.e., projected) into a hologram detector plane 6 of a hologram detector 7. The focusing is accomplished by an ultrasonic lens system 3, which focuses the scattered sound into the hologram detector plane 6 and the unscattered sound into a focal point 4. U.S. Pat. No. 5,235,553 describes an ultrasonic lens that may be satisfactorily used for the ultrasonic lenses illustrated as the lens system 3 in FIG. 1. The ultrasonic lens system 3 also allows the imaging process to magnify the image (i.e., zoom) or change focus position. U.S. Pat. No. 5,212,571 illustrates a lens system that can magnify the image and change focus position and may be used satisfactorily for the lens system 3.
Since the focal point 4 of the unscattered sound is prior to the hologram detector plane 6, this portion of the total sound again expands to form the transparent image contribution (that portion of the sound that transmitted through the object as if it were transparent or semi-transparent). In such an application, an ultrasound reflector 5 is generally used to direct the object sound at a different angle, thus impinging on the hologram detector plane 6, which usually contains a liquid that is deformed by the ultrasound reflecting from the liquid-air interface. In an exemplary embodiment, The base of the hologram detector 7 is made to be parallel with the ground so that the thickness of the fluid below hologram plane 6 remains at a constant value.
When a reference wave 8 and the object wave are simultaneously reflected from the hologram detector 7, the deformation of the liquid-air interface is the exact pattern of the ultrasonic hologram formed by the object wave (1a combined with 2a) and the xe2x80x9coff-axisxe2x80x9d reference wave 8. This ultrasonic hologram formed on the detector plane 6 is subsequently reconstructed for viewing by using a coherent light source 9, which may be passed through an optical lens 10, and reflected from the holographic detector plane 6.
This reflected coherent light contains two components. The first component is light that is reflected from the ultrasound hologram that was not diffracted by the ultrasonic holographic pattern, which is focused at position 11 and referred to as undiffracted or zero order light. The second component is light that does get diffracted from/by the ultrasonic hologram is reflected at an xe2x80x9coff-axisxe2x80x9d angle from the zero order at position 12 and referred to as the xe2x80x9cfirst orderxe2x80x9d image view when passed through a spatial filter 13. It is noted that this reconstruction method produces multiple diffraction orders each containing the ultrasonic object information. Note also both + and xe2x88x92 multiple orders of the diffracted image are present and can be used individually or in combinations to view the optical reconstructed image from the ultrasonically formed hologram by modifying the spatial filter 13 accordingly. The hologram detector 7, coherent light source 9, optical lens 10, and spatial filter 13 may be referred to in combination as a detector system 15.
It is apparent from the understanding of the operation of acoustical holography that the anatomy of the patient needs to be inserted into the path of the acoustical energy that is referred to as the object wave. Furthermore, the system must remain stable during operation. The present invention provides this and other advantages as will be apparent from the following detailed description and accompanying figures.
The present invention is embodied in a system and method that improves reliability and simplifies operation of diagnostic imaging. In one aspect, the invention is embodied in a system for stabilizing an image detector that is configured to receive acoustic signals and comprises a base member and a mounting platform fixedly coupled to the base member. A leveling plate supports the image detector and a plurality of adjustable leveling members having first and second ends couple the leveling plate to the mounting platform. The first end of each leveling member is coupled to the mounting platform and the second end of each leveling member is coupled to the leveling plate. A level sensor assembly detects an orientation of the leveling plate and generates sensor signals related thereto. A controller responds to the sensor signals to generate leveling control signals and a drive mechanism coupled to at least a portion of the leveling members responds to the leveling control signals to position the leveling plate at a predetermined orientation.
In an exemplary embodiment, the level sensor assembly and drive mechanism form a feedback circuit. The level sensor assembly may comprise first and second level sensors that are positioned in a substantially orthogonal arrangement on the leveling plate to sense variations in the first and second substantially orthogonal directions.
In another aspect, an imaging system generates an image of patient anatomy and has a predetermined area of imaging coverage and is focused at a predetermined focal plane. The system comprises a three-dimensional drive system to control position of the patient in three dimensions with the drive system operating in two dimensions to position a selected anatomical feature of the patient at a desired location within the predetermined area of imaging coverage and operating in a third dimension to position the selected anatomical feature of the patient at a desired plane substantially parallel with the predetermined focal plane. The system further comprises a rotational drive system to permit rotation of the selected anatomical feature about an axis of rotation substantially within the desired plane wherein the selected anatomical feature is imaged within the predetermined area of imaging coverage and about the axis of rotation.
In one embodiment, the imaging system may comprise an ultrasound imaging system or may be used with an x-ray imaging system.
In another aspect, the imaging system has an adjustable focus and is readjusted such that the readjusted focal plane coincides with the desired plane. This allows the selected anatomical feature to be viewed as the rotational drive system rotates the anatomical feature.